The present invention relates to torque transmitting fluid couplings, and more particularly, to such a coupling which utilizes a temperature-responsive bimetal coil to control the position of a valve which, in turn, controls the flow of fluid within the coupling.
Fluid couplings of the type to which the present invention relates are now well-known in the art and may be better understood by reference to U.S. Pat. Nos. 3,055,473, 3,174,600, and 3,339,689, assigned to the assignee of the present invention. Briefly, such fluid couplings typically include a coupling body which defines a fluid chamber, a coupling member rotatable relative to the coupling body, the body and member each including a plurality of concentric annular lands alternately positioned such that rotation of the coupling member causes the viscous fluid in the operating chamber and between the lands to exert a viscous drag on the coupling body, thereby rotating the body. The coupling also includes a valve plate and a cover, the valve plate dividing the chamber into a fluid operating chamber and a fluid reservoir chamber. The valve plate defines a fluid inlet port which permits fluid to pass from the reservoir chamber to the operating chamber, and a fluid discharge port which permits fluid to pass from the operating chamber to the reservoir chamber. A valve member controls the flow of fluid through the inlet port and discharge port in response to the atmospheric temperature external to the coupling. Typically, the valve member is mounted on a shaft which is rotatable relative to the cover, with one end of the bimetal coil being fixed to the shaft and the other end fixed relative to the cover by means of a bracket assembly.
Conventionally, the cover, bimetal coil, valve shaft, valve member and valve plate are assembled as a unit with the correctness of the position of the valve plate relative to the rest of the subassembly being determined by means of a water bath test wherein the bimetal coil is subjected to water at a predetermined temperature, usually the temperature at which it is intended that the valve member begin to uncover the inlet port to permit fluid to enter the operating chamber.
Subsequent to this testing operation, the remainder of the coupling is assembled, after which the entire assembly is tested under actual operating conditions. At this point, it is frequently determined that engagement of the coupling does not actually occur within the prescribed temperature range, either because the setup of the water bath test was improper or defective, or for any other reason. When such is the case, it is necessary either to scrap the entire coupling assembly, or to forceably disassemble it in an attempt to salvage some of the parts, typically, only such items as the bimetal coil and bearing set. The need to scrap almost the entire coupling assembly is clearly undesirable in any case, but especially, on those couplings such as for trucks, which are larger and more expensive to manufacture.